more docs

docs/MIGRATION.md

@@ -3,6 +3,7 @@
 - [Migration](#migration)
   - [Multiple uploads to the same named Artifact](#multiple-uploads-to-the-same-named-artifact)
   - [Overwriting an Artifact](#overwriting-an-artifact)
+  - [Merging multiple artifacts](#merging-multiple-artifacts)
 
 Several behavioral differences exist between Artifact actions `v3` and below vs `v4`. This document outlines common scenarios in `v3`, and how they would be handled in `v4`.
 
@@ -142,3 +143,64 @@ jobs:
 ```
 
 Note that this will create an _entirely_ new Artifact, with a different ID from the previous.
+
+## Merging multiple artifacts
+
+In `v3`, multiple uploads from multiple jobs could be done to the same Artifact. This would result in a single archive, which could be useful for sending to upstream systems outside of Actions via API or UI downloads.
+
+```yaml
+jobs:
+  upload:
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - name: Create a File
+        run: echo "hello from ${{ matrix.runs-on }}" > file-${{ matrix.runs-on }}.txt
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: all-my-files # NOTE: same artifact name
+          path: file-${{ matrix.runs-on }}.txt
+```
+
+The single `all-my-files` artifact would contain the following:
+
+```
+.
+  ∟ file-ubuntu-latest.txt
+  ∟ file-macos-latest.txt
+  ∟ file-windows-latest.txt
+```
+
+To achieve the same in `v4` you can change it like so:
+
+```diff
+jobs:
+  upload:
+    strategy:
+      matrix:
+        runs-on: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - name: Create a File
+        run: echo "hello from ${{ matrix.runs-on }}" > file-${{ matrix.runs-on }}.txt
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v3
+        with:
+-         name: all-my-files
++         name: my-artifact-${{ matrix.runs-on }}
+          path: file-${{ matrix.runs-on }}.txt
++ merge:
++   runs-on: ubuntu-latest
++   needs: upload
++   steps:
++     - name: Merge Artifacts
++       uses: actions/upload-artifact/merge@v4
++       with:
++         name: all-my-files
++         pattern: my-artifact-*
+```
+
+Note that this will download all artifacts to a temporary directory and reupload them as a single artifact. For more information on inputs and other use cases for `actions/upload-artifact/merge@v4`, see [the action documentation](../merge/README.md).

merge/README.md

@@ -7,6 +7,10 @@ Merge multiple [Actions Artifacts](https://docs.github.com/en/actions/using-work
     - [Inputs](#inputs)
     - [Outputs](#outputs)
   - [Examples](#examples)
+    - [Combining all artifacts in a workflow run](#combining-all-artifacts-in-a-workflow-run)
+    - [Prefix directories in merged artifact](#prefix-directories-in-merged-artifact)
+    - [Deleting artifacts after merge](#deleting-artifacts-after-merge)
+    - [Retention and Compression Level](#retention-and-compression-level)
 
 ## Usage
 
@@ -15,6 +19,10 @@ Merge multiple [Actions Artifacts](https://docs.github.com/en/actions/using-work
 
 Note: this actions can only merge artifacts created with actions/upload-artifact@v4+
 
+This sub-action is a helper to merge multiple artifacts after they are created. To do so, it will download multiple artifacts to a temporary directory and reupload them as a single artifact.
+
+For most cases, this may not be the most efficient solution. See [the migration docs](../docs/MIGRATION.md#multiple-uploads-to-the-same-named-artifact) on how to download multiple artifacts to the same directory on a runner. This action should only be necessary for cases where multiple artifacts will need to be downloaded outside the runner environment, like downloads via the UI or REST API.
+
 ### Inputs
 
 ```yaml
@@ -60,4 +68,133 @@ Note: this actions can only merge artifacts created with actions/upload-artifact
 
 ## Examples
 
-TODO(robherley): add examples
+For each of these examples, assume we have a prior job matrix that generates three artifacts: `my-artifact-a`, `my-artifact-b` and `my-artifact-c`.
+
+e.g.
+
+```yaml
+jobs:
+  upload:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        foo: [a, b, c]
+
+    steps:
+      - name: Run a one-line script
+        run: echo "hello from job ${{ matrix.foo }}" > file-${{ matrix.foo }}.txt
+      - name: Upload
+        uses: actions/upload-artifact@v4
+        with:
+          name: my-artifact-${{ matrix.foo }}
+          path: file-${{ matrix.foo }}.txt
+```
+
+Each of the following examples will use the `needs: upload` as a prerequesite before any merging operations.
+
+### Combining all artifacts in a workflow run
+
+By default (with no inputs), calling this action will take all the artifacts in the workflow run and combined them into a single artifact called `merged-artifacts`:
+
+```yaml
+jobs:
+  # ... <upload job> ...
+  merge:
+    runs-on: ubuntu-latest
+    needs: upload
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+```
+
+This will result in an artifact called `merged-artifacts` with the following content:
+
+```
+.
+  ∟ file-a.txt
+  ∟ file-b.txt
+  ∟ file-c.txt
+```
+
+To change the name of the artifact and filter on what artifacts are added, you can use the `name` and `pattern` inputs:
+
+```yaml
+jobs:
+  # ... <upload job> ...
+  merge:
+    runs-on: ubuntu-latest
+    needs: upload
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          name: my-amazing-merged-artifact
+          pattern: my-artifact-*
+```
+
+### Prefix directories in merged artifact
+
+To prevent overwriting files in artifacts that may have the same name, you can use the `separate-directories` to prefix the extracted files with directories (named after the original artifact):
+
+```yaml
+jobs:
+  # ... <upload job> ...
+  merge:
+    runs-on: ubuntu-latest
+    needs: upload
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          separate-directories: true
+```
+
+This will result in the following artifact structure:
+
+```
+.
+  ∟ my-artifact-a
+    ∟ file-a.txt
+  ∟ my-artifact-b
+    ∟ file-b.txt
+  ∟ my-artifact-c
+    ∟ file-c.txt
+```
+
+### Deleting artifacts after merge
+
+After merge, the old artifacts may no longer be required. To automatically delete them after they are merged into a new artifact, you can use `delete-merged` like so:
+
+```yaml
+jobs:
+  # ... <upload job> ...
+  merge:
+    runs-on: ubuntu-latest
+    needs: upload
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          delete-merged: true
+```
+
+After this runs, the matching artifact (`my-artifact-a`, `my-artifact-b` and `my-artifact-c`) will be merged.
+
+### Retention and Compression Level
+
+Similar to actions/upload-artifact, both [`retention-days`](../README.md#retention-period) and [`compression-level`](../README.md#altering-compressions-level-speed-v-size) are supported:
+
+```yaml
+jobs:
+  # ... <upload job> ...
+  merge:
+    runs-on: ubuntu-latest
+    needs: upload
+    steps:
+      - name: Merge Artifacts
+        uses: actions/upload-artifact/merge@v4
+        with:
+          retention-days: 1
+          compression-level: 9
+```